I. Field of the Invention
My invention relates generally to high pressure fittings and check valves. More particularly, the invention relates to high pressure check valves and grease fittings equipped with internal valve-centering structures for maintaining component alignment, and preventing internal structural deformation, when subject to extremely high operating pressure. Known prior art can be found in United States Patent Class 137, Subclass 539.
II. Description of the Prior Art
Numerous high pressure lubrication fittings and check valves exist in the art. Such fittings are common in heavy industrial equipment, construction vehicles, and oil and gas apparatus. These high pressure devices are known in the art as check-valves, sealant fittings, lubrication adapters, and button head fittings. They facilitate the injection of a variety of conventional and synthetic greases, lubricants and/or sealants, which are injected periodically during equipment maintenance. Their primary function is to accept and channel lubricants and/or sealants to the correct inner working parts of the apparatus upon which they are mounted. Heavy duty applications often involve pressures exceeding fifteen thousand (15,000) PSI. Typical high pressure grease fittings such as "button-head" fittings are widely used in the oil and gas industry. A button-head fitting allows the grease or injection gun to be securely fastened within the fitting inlet as lubricant is forcefully injected.
However, common button-head fittings and high pressure check valves suffer from numerous disadvantages. As explained in my prior U.S. Pat. No. 4,977,927, button-head fittings can internally deform in response to the injection of heavy sealants or lubricants. Some prior art fittings employ a "soft seat" formed by a steel ball which forcibly contacts a non-metallic element to form a one-way valve. Soft seats can wear out quickly when subjected to sustained pressures. At high pressures, the seat against which the valve ball presses can distort, resulting in leaks through the fitting. The apparatus on or in which the fittings may be used might have internal leakage. The causes for internal leakage are many and varied. Causes include accumulated wear on moving, mating parts, and damages from corrosive or abrasive gases or liquids. Some OEM designs are insufficient to prevent leakage. Whatever the cause, an important function of every pressure fitting is to prevent back pressure leakage through itself. It is a common practice to seal the leak paths by injecting lubricants containing bridging agents such as plastics, TFE fluorocarbons, etc. However, bridging agents cause other problems.
The injection of heavy bridging agents can bend or misalign conventional valve return springs, which are structurally located proximate the material flow path internally of the fitting. So-called "plug-off" or clogging can result, since the return spring forms a grease flow path through which at least a portion of the lubricants or sealants may normally flow. If the check valve ball over-compresses the return spring, the flow path may be impeded. Blocking or clogging raises the internal fluid pressure, and the spring may be permanently deformed as a result. Spring damage also results from "cylinderization," which can occur when the return spring is longitudinally compressed until its adjacent windings are squeezed together to form a cylinder-like tube. Cylinderization severely restricts grease outflow through the adjacent spring, windings, which should normally be spaced-apart.
Another problem relates to part misalignment. Over time, in response to high pressures and component wear, the check valve ball may reposition itself atop the compressed spring in an offset position. In this instance, the ball center is offset from the longitudinal axis of the return spring. As a result, injection pressures are not properly dissipated, and the valve does not seat optimally. Leaking is commonly the result. In cases of extreme wear or component deformation, dangerous "blow-out" can occur. In response, internal parts of the fitting may explode outwardly. Sometimes the damaged parts are forced into the attached equipment or pipeline. During the resultant down time they must be removed from the flow path, and the damaged fitting must be replaced. The blow-down process is time-consuming and expensive. Those skilled in the art will recognize a number of other problems experienced eventually by typical high pressure fittings.
U.S. Pat. No. 4,347,915 employs an offset spring "leg" to cause the ball member to drift to one side when the spring compresses. However, heavy sealants with large bridging agents cause the leg member to bend laterally, trapping the ball, and preventing it from reseating properly. Spring deformation can result.
U.S. Pat. Nos. 2,918,084 and 3,437,082 disclose a variety of spring, ball, and sleeve configurations.
The high pressure fitting disclosed in my prior U.S. Pat. No. 4,977,927 was designed to prevent spring deformation and cylinderization. A rigid retainer, generally in the form of a parallelepiped, is threadably received within the tubular fitting, outlet. A rigid, integral stem projecting from the retainer coaxially receives and mounts the valve spring, which normally biases the ball towards the valve seat.
However, my subsequent experiments have revealed that there is ample room for improvement. For example, despite the fact that longitudinal spring compression stops when the check valve ball contacts the projecting stem, lateral spring deformation can still occur with my prior design. Such deformation can result during assembly, when the threaded retainer is forcibly rotated. Further, retainer integrity is limited by its threaded design. Finally, after extreme use, dissected fittings reveal check valve ball misalignment. In other words, the valve balls have become slightly offset relative to the longitudinal axis of the spring and the projecting stem. As mentioned above, valve ball offsetting degrades check valve sealing.
It is also important to eliminate the cold working of metals. The term "cold working" refers to the physical deformation of metal at room temperature. For fittings adapted for non corrosive applications, the manufacturing process often involves the crimping or deforming of metal to capture or retain valve springs. Metals used for Sour Service are subject to sulfide stress cracking caused by hydrogen sulfide. Cold-worked parts are subject to stress cracking, and their use should be avoided. Unfortunately, many prior art designs include cold-worked parts.
Therefore, I have designed an improved high pressure fitting. Critical interior parts dynamically control the operative positions of the check-valve ball and the return spring. Dynamic ball centering occurs while an adequate flow path is preserved. The new system substantially attenuates spring deformation and cylinderization, while concurrently preventing valve offset. Dynamic interaction of the preferred parts, including a dynamic spring mounting system and a self-centering check valve ball seating arrangement, enhances fitting performance and durability. The new design increases component life, enhances fluid flow rates, and encourages leak-proof valve sealing.